1. Field of the Invention
The present invention relates to a combustion device for improving a turndown ratio, and more particularly, to a combustion device for improving a turndown ratio, in which a venturi structure is designed into multiple stages, and the venturi configuration varies to improve a turndown ratio, as well as, when the air and gas are premixed with each other in a premixing chamber, a passage of gas and air is formed so that the gas is discharged in the same direction as a flow direction of the air to stably implement a combustion state even at a low-output load region.
2. Description of the Related Art
In general, a turndown ratio (TDR) of a burner is set for gas combustion devices such as gas boilers or gas water heaters. The TDR refers to a ‘ratio of the maximum gas consumption to the minimum gas consumption’ in a gas combustion device in which a gas amount is variably regulated. For example, when the maximum gas consumption is 30,000 kcal/h, and the minimum gas consumption is 6,000 kcal/h, the TDR becomes 5:1. The TDR may be limited according to the lowest adjustable level of the minimum gas consumption in order to maintain stable flame.
In the case of the gas combustion device, convenience in use during a heating and hot-water operation increases as the TDR increases. That is, initial combustion is performed with a maximum thermal power to reach a desired heating temperature within a short time. However, when the heating temperature reaches close to the desired heating temperature, an amount of gas supplied into a burner may be reduced to perform the combustion. Here, when the TDR is less due to the high minimum gas consumption, it is difficult to control the reduction of the gas amount so as to reduce the output of the burner.
In particular, when the burner operates in low heating and hot-water load region, the combustion device may be frequently turned on/off, and thus the combustion state may be unstable. As a result, a variation in a temperature control increases to deteriorate durability of the device. Therefore, methods for improving the TDR of the burner that are applied to combustion devices have been proposed.
As the related prior art, Korean Patent Registration No. 10-0805630 discloses a combustion device for a gas boiler that includes a blower for supplying air required for combustion, a proportional control valve for regulating a flow rate of supplied gas, a nozzle unit connected to the proportional control valve to supply a gas through an opening/closing of an auxiliary valve, the nozzle unit including a plurality of nozzles that are connected in parallel to each other, a mixing chamber in which the air supplied from the blower and the gas passing through the nozzle unit are mixed with each other to supply the mixture onto a surface of the burner, and a control unit for controlling the number of revolution of the blower through an opening/closing of the proportional control valve and the auxiliary valve to supply only a required amount of air for combustion.
According to the above-described constitutions, there is an advantage in that the nozzles of the nozzle unit into which the gas is supplied are parallely disposed in multiple stages, and the opening/closing of each of the nozzles is controlled to correspond to an output of the burner to improve a turndown ratio, thereby enhancing combustion stability in a low-output load region.
However, in conventional combustion devices in addition to the prior art, a relationship between flow directions of air and gas when the air and gas are mixed with each other in the mixing chamber (premixing chamber) and combustion efficiency have not been considered. In the conventional combustion devices, the flow direction of the air and the discharge direction of the gas in the premixing chamber are different from each other to mix the air and the gas with each other. Thus, when the gas is discharged in a direction different from the flow direction of the air to mix the gas with the air, the gas discharge is effected by the air flow. As a result, it may be difficult to obtain a desired air/gas ratio, and thus unstable combustion may occur to deteriorate low combustion efficiency.
Also, since the premixing chamber of the conventional combustion device has a single venturi structure, the TDR is limited to a ratio of 5:1 or less. Thus, when burned in a low-output load region, the burner may be frequently turned on/off to deteriorate the combustion efficiency, thereby deteriorating the performance of the combustion device.